diff --git a/includes/stg/Prim.h b/includes/stg/Prim.h
index 2b23c3d4c70609e69ebb14143df57503809b6555..7d94d1846daab4cb930fc21fb97677cafdd1ed19 100644
--- a/includes/stg/Prim.h
+++ b/includes/stg/Prim.h
@@ -22,14 +22,14 @@ StgWord64 hs_bswap64(StgWord64 x);
 /* TODO: longlong.c */
 
 /* libraries/ghc-prim/cbits/popcnt.c */
-StgWord hs_popcnt8(StgWord8 x);
-StgWord hs_popcnt16(StgWord16 x);
-StgWord hs_popcnt32(StgWord32 x);
+StgWord hs_popcnt8(StgWord x);
+StgWord hs_popcnt16(StgWord x);
+StgWord hs_popcnt32(StgWord x);
 StgWord hs_popcnt64(StgWord64 x);
 #ifdef i386_HOST_ARCH
-StgWord hs_popcnt(StgWord32 x);
+StgWord hs_popcnt(StgWord x);
 #else
-StgWord hs_popcnt(StgWord64 x);
+StgWord hs_popcnt(StgWord x);
 #endif
 
 /* libraries/ghc-prim/cbits/word2float.c */